A fundamental question in connection with the dynamo mechanism is how to retain the magnetic flux in the convection zone (or below) for a time sufficiently long to be amplified by differential rotation. Magnetic buoyancy poses a serious problem, for it might lead to a rapid loss of magnetic flux from the convection zone and thus prevent the operation of the dynamo.

Apart from observations of the solar surface, there are indirect hints for the existence of a strong toroidal system of magnetic flux at the bottom of the solar convection zone. The concentration of magnetic flux into flux tubes has important consequences for its storage. In this context, the stability of toroidal flux tubes has been subject of research since the 1980's, starting with Spruit and van Ballegooijen (1982).

In this talk I will report on an ongoing investigation which extends previous research on the stability properties of a thin toroidal flux tube. A new feature is the inclusion of external velocity fields other than rotation; this is motivated by the necessity of including the effects of a meridional flow into the stability analysis.